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Posted 31 Oct 2013

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Generic Event Handler Using Extension Method

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2.22/5 (4 votes)
31 Oct 2013CPOL
A handy approach to raise events.

Introduction

Very often we need to invoke events, usually in Model classes , where we set some property and raise an event in order to notify any listeners. 

Using the code

Following is a full length example of 'How to use a Generic Event Handler to Raise an Event'.

It is good to have some helper (extension) method that can be used at various places, thus reducing the amount of code and making it quite maintainable.

C#
using System;
using ExtensionHelper;

namespace EventHandlers
{
    public class MyModel
    {
        private string _name;
        private int _age;
        private decimal _salary;

        MyModel() { }

        public string Name
        {
            get { return _name; }
            set 
            {
                _name = value;
                NameChanged.Raise(this, EventArgs.Empty);
            }
        }

        public int Age 
        { 
            get { return _age; } 
            set 
            {
                _age = value;
                AgeChanged.Raise(this, EventArgs.Empty);
            } 
        }

        public decimal Salary 
        { 
            get { return _salary; } 
            set 
            { 
                _salary = value;
                SalaryChanged.Raise(this, EventArgs.Empty);
            }
        }

        public EventHandler NameChanged;
        public EventHandler AgeChanged;
        public EventHandler SalaryChanged;

    }

}

namespace ExtensionHelper
{
    public static void Raise(this EventHandler eventHandler, object sender, EventArgs e)
    {
        if (eventHandler != null)
        {
             eventHandler(sender, e);
        }
    }

    public static void Raise<T>(this EventHandler<T> eventHandler, 
           object sender, T e) where T : EventArgs
    {
        if (eventHandler != null)
        {
            eventHandler(sender, e);
        }
    }
}

History

This is my first article on CodeProject, and I am using the above mentioned code in my current assignments.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


Written By
Software Developer
India India
I am a Software Developer By Profession.

Comments and Discussions

 
GeneralMy vote of 1 Pin
Athari1-Nov-13 5:25
Athari1-Nov-13 5:25 
GeneralMy vote of 1 Pin
johannesnestler1-Nov-13 0:49
johannesnestler1-Nov-13 0:49 
QuestionThere is also a possibility for null exception there due to a well known race condition when dealing with events Pin
Sacha Barber31-Oct-13 7:03
Sacha Barber31-Oct-13 7:03 
AnswerRe: There is also a possibility for null exception there due to a well known race condition when dealing with events Pin
Athari31-Oct-13 9:58
Athari31-Oct-13 9:58 
GeneralRe: There is also a possibility for null exception there due to a well known race condition when dealing with events Pin
johannesnestler1-Nov-13 0:14
johannesnestler1-Nov-13 0:14 
GeneralRe: There is also a possibility for null exception there due to a well known race condition when dealing with events Pin
Athari1-Nov-13 2:48
Athari1-Nov-13 2:48 
GeneralRe: There is also a possibility for null exception there due to a well known race condition when dealing with events Pin
johannesnestler1-Nov-13 4:44
johannesnestler1-Nov-13 4:44 
GeneralRe: There is also a possibility for null exception there due to a well known race condition when dealing with events Pin
Athari1-Nov-13 5:03
Athari1-Nov-13 5:03 
GeneralRe: There is also a possibility for null exception there due to a well known race condition when dealing with events Pin
johannesnestler1-Nov-13 5:53
johannesnestler1-Nov-13 5:53 
Ah now I see what you missed: We are talking about multithreaded scenario! And btw. what Jon Skeet is writing there (don't know him, just saw his posts on the linked site, add extra handler to avoid null check, classes should be sealed etc.) I think I can honestly say I'm a smarter programmer (but thats not my point, just giving you an answer).

Provide code for what? Sasha showed the point, you commented he is wrong (you know that Sasha is one of the heroes here?), I told you you are wrong, you linked to "not so good" postings about the topic...

Btw as I mentioned this is a VERY WELL known topic in .NET and therefore this pattern (to create a local copy) emerged. You didn't know it, that's ok, and if you still write your code like Jon Skeet, I have no problem with that too (And if you don't do any multithreading and only simple apps it's ok too).

But you are right it shouldn't need to be done like this, I'd call it a "design flaw" in .NET.
GeneralRe: There is also a possibility for null exception there due to a well known race condition when dealing with events Pin
Athari1-Nov-13 6:31
Athari1-Nov-13 6:31 
GeneralRe: There is also a possibility for null exception there due to a well known race condition when dealing with events Pin
johannesnestler1-Nov-13 8:34
johannesnestler1-Nov-13 8:34 
AnswerRe: There is also a possibility for null exception there due to a well known race condition when dealing with events Pin
Bheeshm31-Oct-13 16:49
professionalBheeshm31-Oct-13 16:49 
QuestionNot following the convention... Pin
johannesnestler31-Oct-13 5:57
johannesnestler31-Oct-13 5:57 
AnswerRe: Not following the convention... Pin
OriginalGriff31-Oct-13 6:37
mvaOriginalGriff31-Oct-13 6:37 
AnswerRe: Not following the convention... Pin
Bheeshm31-Oct-13 16:55
professionalBheeshm31-Oct-13 16:55 
GeneralRe: Not following the convention... Pin
johannesnestler1-Nov-13 0:46
johannesnestler1-Nov-13 0:46 
GeneralRe: Not following the convention... Pin
Bheeshm1-Nov-13 2:23
professionalBheeshm1-Nov-13 2:23 
GeneralRe: Not following the convention... Pin
johannesnestler1-Nov-13 5:00
johannesnestler1-Nov-13 5:00 
GeneralRe: Not following the convention... Pin
Athari1-Nov-13 5:20
Athari1-Nov-13 5:20 
GeneralRe: Not following the convention... Pin
johannesnestler1-Nov-13 5:59
johannesnestler1-Nov-13 5:59 

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